analysis of self excited induction generator

7/30/2019 Analysis of Self Excited Induction Generator

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390 IEEE Transactions on Energy Conversion, Vol. 9, No. 2, June 1994ANALYS IS OF SELF EXCITED INDUCTION GENERATO RFEEDING INDUCTION M O T O R

L. Shridhar, Student Member, Bhim Singh, C. S. Jha and B.P. Singh, SMDepartment of Electrical Engineering, IIT Delhi, Hauz KhasNew Delhi 110 016, FAX 91-11-6862037, INDIAAb st ra ct The paper is motivated to assess the 2. INTRODUCTIONsuitability of a self excited induction generator(S EI G) to supply dynamic loads like induct ion Self Excited Induction Generators (SEIGs) aremotors. An algorithm is proposed to Predict the increa singly being consid ered for autono moussteady state performance of an SEIG feeding anr e s u l t s a r e p r e s e n t e d f o r d i f f e r e n t o p e r a t i n g p o w e r ed s y s t e m s T h e lower unitcond itio ns of an SEIG-IM system. A good agreement brus hles s cage rotor construction, absence of areache d betwe en th e predict ed and test results separate dc source, better transient performancev a l i d a t e t h e e f f e c t i v e n e s s o f t h e p r o p o s e d a n d i n h e r e n t o v e r l o a d p r o t e c t i o n a r e i t s m a i nalgorithm. advantages over the conventional alternators.It is well known that if an appropriatexperimentally recorded transients of an SEIGd u r i n g a S e r i e s O f s w i t c h i n g O p e r a t i o n s a r e capacitor bank is connected across an externallypresented to demonstrate the ability of an SEIG to driven induction machine, an EMF is induced in thesustain the starting of an IM.By analyzing the performance of a typical 7.5 machine windings due t o the excitation provided byk W , 3 -ph ase SEIG feeding induct ion moto rs of the Capacitor. The induced voltage and currentdifferent ratings, useful guidelines are proposed would continue to rise, until the var supplied byfor the design of an SEIG-IM system in aU to "m us the capacitor is balanced by the var demanded byapplicatio ns like agricultu ral pumpsets. the machine. Thi s results in an equilibriu m statebeing reached and t he machine now operates as an

value of the capacitor, speed of the prime mover,parameters of the machine and the load [1,2].A m a j o r i t y o f s y s t e m l o a d s i s d y n a m i c i nnature, v arying both in quantit y and quality.Contribution of induction motors(1Ms) to such loads

i s s i g n i f i c a n t . A r e v i e w of t h e a v a i l a b l eliterature reveals that although a lot of work hasbeen reported on the SEIG feeding static loads,prediction of its behavior while feeding an IMremains to be properly explored. Behavior of theSEIG feeding an ind uction motor is of interest notonly from the operationa l point of view but alsofrom the view point of assessing its suitability tofeed such loads. Further, it will be desirable tos t u d y t h e a b i l i t y o f t h e S E I G t o w i t h s ta n dswitching of dynamic loads, such as, starting of

P r e d i c t i o n o f o p e r a t i n g f r e q u en c y , F a n despective generator quantities, except, the outputpower of the motor and the system var for which the satu rat ion level (an d hence t h e v a l u e o frated mot or Power and gen era tor power, magnetizing reactance, Xm) of an SEIG is the first

step in its analysis. For an SEIG feeding a staticespective ly, are taken as base quantities.R L l o a d , v a r i o u s t e c h n i q u e s a r e a v a i l a b l e t o93 SM 4 53-1 EC estimate values of the se two unknowns (F and Xm)

by the IEEE Electric Machinery Committee of the [ 3 , 4 , 6 - 9 1 .IEEE Power Engineering Society for presentation When a n IM is fed from an SEIG, apart from Xmand F; slip and saturation level of the motor ar eCanada, July 18-22, 1993. Manuscript submitted Aug.28, 1992; made available for printing 12, 1993. unknowns to be evaluated before its performance canbe determined. The identification of these fourPRINTED IN USA parameters becomes complicated, as the methods usedwith an SEIG feeding static loads are not directlyappl icab le to an SEIG-IM systems. Thus, to predictp e r f o r m a n c e o f a n S E I G - I M s y s t e m f o r a g i v e n

operating condition , it is necessary to develop asuitable analytical technique.This paper is addressed to the analysis of the

SEIG feeding power to an induction motor. Analgorithm is proposed t o predict the performance ofan SEIG-IM system. The predicted and experiment alr e s u l t s a r e p r e s e n t e d f o r d i f f e r e n t o p e r a t i n gc o n d i t i o n s . T h e s e l e c t i o n o f c a p a c i t o r f o r t h estarting of th e motor is discussed and experimentalresults are presented for a sequence of the IMswitchings on an SEIG. The study is extended tocover a range of standard motors to confirm theg e n e r a l t r e n d . B a s e d o n t h e a n a l y s i s , u s e f u lguidelines are provided for designing an autonomousS E I G - IM s y s t e m f o r a p p l i c a t i o n s l i k e a nagricultural pumping system.

induction (IM). The computed and experimental app lic ati ons in micro-hydro. biogas and wind

Keywords: Autonomous Power Generation, Induction SEIG at a volt age and frequency decided by theGenerator, Capacitor Self Excitation, Analysis1. NOMENCLATURE

Main Symbols: Subscripts:c capacitance/phase c capacitiveF p.u. freq uenc y g air gapI p.u. curr ent 1 leakageP p.u. pow er L loadR p.u. resi stan ce out outputs slip of the motor r rotorv p.u. volt age s statorX p.u. reac tanc e M motorz p. U. impedance~ l l . u . quanti ties are at the b ase of induction motors.

p.u. speed t term inal

A paper recommended and approved

at the IEEEIPES 1993 "=r Meeting, Vancouve r, B.C. , also unknown. Th e SEIG-IM system t h u s has four

0885-8969/94/$04.000 1993 IEEE


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39 1a n d a r e o b t a i n e d b y s i m p l i f y i n g e q u a t io n ( 3 ) [ 4 ) .N o w t h e p e r f o r m a n c e o f t h e SEIG c a n b e o b t a i n e d a sf o l l o w s :

3. THEORYH e r e , a t f i r s t t h e te c hn i qu e [ 3 , 4 ] u s ed f o r

t h e a n a l y s i s o f a n SEIG f e e d i n g a s t a t i c RL l o a d i sb r i e f l y d i s c u s s e d ; w h i ch i s t h e n e x t e n d e d t od e v e l o p a n a l g o r i t h m f o r a n a l y z i n g a n S EIG-IMs y s t e m .3 .1 Static RL Load

T h e s t e a d y s t a t e re sp onse o f an SEIG feed in g as t a t i c RL l o a d c a n be p r e d i c t e d f o r a ny pr i m e mo ve rs p ee d , c a p a c i t a n c e a n d l o a d c o n d i t i o n s f ro m t h ee q u i v a l e n t c i r c u i t o f F i g u r e l ( a ) , i f a l l i t sp a r a m e t e r s a r e k no wn . O n l y t h e m a g n e t i z i n gr e a c t a n c e , i s a s s u m e d t o b e a f f e c t e d b y t h em a g n e t i c s a t u r a t i o n , a n d a l l o t h e r e q u i v a l e n tc i r c u i t p a r a m et e r s o f t h e ma ch in e a r e assumed t o b ec o n s t a n t . I t c a n b e n o te d t h a t a l l p a r a m e t e r se x c e p t X,, a r e k no wn e i t h e r f r om e x p e r i m e n t a t i o no r d e s i g n . H ow ev er , t h e v a r i a t i o n o f X w i t h V / F( a m e as u re o f m a g n e t ic f l u x l e v e l ) , i s a v a i l a g l e[3]. F u r t h e r , t h e g e n er a t e d f r e qu e n cy i s a l s ou nk no wn . E s t i m a t i o n o f X, a n d F i s a s p e c i a lp r o bl e m i n t h e a n a l y s i s o f a n SEIG sy s t em .

I I I 1 f

1. V a l u e s o f X, a n d F c an b e o b t a i n e d by s o l v i n gt h e s i m u lt a n e o us e q u a t i o n s ( 4 ) an d ( 5 ) , u s i n g as u i t a b l e n um e r i ca l t e c h n i q u e.2. A f t e r o b t a i n i n g X a n d F , V c a n b e c o m p u t edf ro m t h e m ag n e t i za t i o n c h a r a % t e r i s t i c s o f t h em a c h i n e .

Vg , i s k no wn , t h e r e q u i r e d p e r f o r m a n c e c a nb e d e t e r m i n e d u s i n g t h e s t a n d a r d e q u a t i o n s 1 41 .

3. Once

3.2 Induction Motor LoadF i g u r e l ( b ) s how s t h e e q ui v a l e n t c i r c u i t o f a n

SEIG-IM system. Here, X F, Xm and s are t h efou r unknowns . The me thodo logy d iscu ssed above fo rt h e s t a t i c RL load g i v e s two e q u a t i o ns ( 4 ) a nd (5),w h i c h a r e s o l v a b l e f o r o n l y t wo un kn ow ns . T hef o l l o w i n g a l g o r i t h m i s p r op o se d t o i d e n t i f y X,, F ,XM m a n d s a n d t h e n p r e d i c t t h e p e rf o rm a nc e o f t h eSEIG-IM system.1. A ss um e n o m i n a l v a l u e s o f V t and F.2. F o r a g i v e n p ow er o u t p u t o f t h e motor , o b t a i n

XM m a n d 8 ,3 . O n c e XMm a n d s a r e know n, t h e e q u i v a l e n t c i r c u i t

o f t h e I M i s r e d u c e d t o a n e q u i v a l e n t RL l o a d( F i g u r e l ( c ) ) .

4 . N ow t h e e q u i v a l e n t c i r c u i t o f F i g u r e l ( b ) i st r a n s fo r m e d i n t o t h a t o f F i g u re l ( a ) a n d i s nows o l v e d f o r X, a n d F u s i n g t h e m e th od d e s c r i b e df o r t h e s t a t i c l o a d .

5 . O b t ai n t h e c o r r e sp o n d i ng v a l u e o f Vg a nd t h e nc a l c u l a t e V,

( A p p e n d i x - I ) .

r6. Go t o S t e p 2 w i t h u p d a t e d v a l u e s o f V t a n d F ia nd r e p e a t , u n t i l e r ro r s i n Vt a n d F d u r i n g t w os u c c e s s i v e i t e r a t i o n a r e l e s s t h a n a s m a l lq u a n t i t y ( s a y , e = 1 .OE-04) .

Fig l(a ) Equivalent circuit of SEIG feediw RL b ad

3 .1 .1 Estimation o f Xm and FA p pl y in g K i r c h o f f ' s v o l t a g e l aw t o t h e l o o p

c u r r e n t I, , w e o b t a i n= oIs zs

where Zs i s loo p impedance andzs = z1 + z2 + z3z1 = zr Z m l ( Z r + Z m )Z r = {Rr/(F-Y ) + j X l r >2 = jx, R m / ( R , + jx,)Z2 = Rs + j X l sZ3 = ZL Z c / ( z L + zc)

I I I ISEIG IM

Fig l(b) Equivalent circuit of SEIG feeding Induction Motor

S i n c e u n d e r s t e a d y s t a t e o p e r a t i o n o f t h eSEIG, Is c a n n o t b e e q u a l t o z e r o , RM S ixMIS 'Mlr

2, = 0E q u a t i n g , t h e r ea l a n d i m a g in a r y p a r t s o f ( 3 )t o z er o, t h e f o l lo w i n g t w o n o n l i n e a r e q u a t i o n s w i t h

IMnknowns X and F are o b t a i n e d .f(X,,,,F) = (A1 X + A2)F6 + (A 3 X +A4)F5 + Fig Hc) Cooversion of Induction Motor circuit into equivalent RL element,

(A s Xm + A6)F4 + (A 7 X + A8)F3 +(A 9 Xm + A10)F2 + ( A 1 1 Xm +AlZ)F +A13 Xm + A14 = 0 ( 4 )

F i g u r e l ( d ) sho ws t h e f lo w c h a r t o f t h ea l g o r i t h m . I n s um m ar y, f o r a g i v e n o p e r a t i n g= (B1 X + B2)F5 + ( B 3 X + B4)F4 + c o n d i t i o n , d u r i n g e a c h i t e r a t i o n t h e a l g o r i t h m(B5 X + B6)F3 + ( B 7 X + B8)F2 + r e p l a c e s t h e I M l o a d b y a n e q u i v a l e n t RL l o a d a n d(B g Xm + Blo)F + Bl l X + B12 = 0 (5) s o l v e s f o r t h i s RL l o a d . T he i t e r a t i o n s a r e

c o n t i nu e d w i t h u p d a t in g o f r e l e v a n t q u a n t i t i e s t i l lThe coefficients - and B~ - B~~ in h e t h e c o n ve r g en c e i s o b t a i n e d . T he a l g o r i t h m w a s

a b o v e equations r e func t ions f m a ch i ne a p p l i e d t o v a r i o u s t r i a l s a n d c o n v e r g e n c e w a sp a r a m e t e r s , l o a d i m p ed a n ce , c a p a c i t a n c e a n d s p e e d ; achieved in 3- 5

I ( X m t F )


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3924. RESULTS AND DISCUSSION

This se ction is divided into two sub sections.1. Steady- state operati on of an S E I G - I M system,2. Star tin g of an I M on an S E I G .4.1 Steady-State Operation

T o c h e c k t h e v a l i d it y o f t h e p r o p o s e dalgorithm, extensive experiments were carried outon an S E I G - I M test rig, schematically shown inFigure 2. A standard 3-Phase squirrel cageinduction motor of 10 hp (7.5 kW), 4 pole, 415 V I14 A , del ta connect ed stator with p.u. circuitp a r a m e t e r s R, =0.0493, Rr=0.0409, Xis= X l r =0.1013, Rm = 22.1 and unsaturate d Xm = 2.15; isoperated as an S E I G . The S E I G was driven by a 10 kWdc motor. The induction motors ( I M s ) wereelectrically loaded by coupling them to separatelyexcited dc generators of appropriate rating.Following tes ts were performed on the system usingsuitable instrumentation.1. The S E I G was driven at a fixed speed. For afixed value of capacitor C, the performance wasmonitored for different loads on the inductionmotor.2. Test de scribed in 1 was repeated for dif ferentvalues of C to estimate the most appropriatevalue.3. Tes ts mentioned in 1 and 2 were repeated for

different constant speeds of the prime mover.4. Tests described in 1 - 3 are repeated for motorsof different frame sizes.Detailed characteristics are presented for a5hp induction motor and the same is considered foran elabo rate discussion. However, a set of

c h a r a c t e r i s t i c s i s p r es e n t e d f o r a s e r i e s o fstandard motors.

Calcul ateHotor Sl ip

Obtai nAL and X

II -alcul ate UpdateX, and F U+ and F

Calcul ateU

M

Performm

t

Fig l ( d ) Flow Chart of the Algo rithm for analysis of SEIG-IM system

CAPACITOR . !BANK

Fig 2 Block diagram of the SEIG-IM test rig4.1.1 Load Characteristics

Fig. 3(a) shows variations of terminal voltageand operating frequency with output power of thegenerator for different values of capacitors. Itis seen that it is possible to load the motor up toits rated power on an S E I G of double rating. Alarger capacitor results in enhanced powercapability of the S E I G . However, th e effect of

frequency0.2

0 0.1 0.2 0.3 0.4 0.6 0.8p out (P.U )Fig.3(a) Variation of Voltage and Frequency with Power Output


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393c a p a c i t o r v a r i a t i o n o n t h e f r e q ue n cy is m a r g i n a l .I t i s o b s er v e d f ro m Fi g u r e 3 ( b ) t h a t o v e r t h i sr a n g e o f l o a d i n g , t h e g e n e r a t o r wi n di n g c u r r e n tr e m a i n s w e l l w i t h i n t h e r a t e d v a l u e ( 1 . 0 P . u . ) .C o n s i d e r i n g a maximum p e r m i s s i b l e o p e r a t i n g v o l t a g eVmax = 1 . 1 0 P . u . , f o r a c a p a c i t a n c e o f 5 0P F l p ha s e , t h e r a t e d l o a d o n t h e motor c o r r e s p o n d st o 0 . 4 3 p. u. l o a d o n t h e g e n e r a t o r . F u r t h e r , ag o od a g r e e m e n t i s n o t i c e d b e tw e en t h e t e s t a n dp r e d i c t e d r e s u l t s , s how n b y p o i n t s an d c o n t i n uo u sl i n e s , r e s p e c t i v e l y . F i g u r e 3 ( c ) sh ow s v a r i a t i o n si n v a r a n d c a p a c i t a n c e r e q u i r e m e n t o f t h e SEIG-IMs y st e m w i t h l o a d i n o r d e r t o m a i n t a i n t h e t e r m i n a lv o l t a g e a t 1 . 0 P . u . .

T he f i g u r e a l s o s ho ws t h e v a r i a t i o n i n p ow er -f a c t o r o f t h e l o a d ( IM ) w i t h t h e p ow er o u t p u t . I tma y b e n o t e d t h a t t h e p a t t e r n o f v a r i o u sc h a r a c t e r i s t i c s o f t h e S EIG w i th a n IM l o a d i ss i m i l a r t o t h a t w i t h a s t a t i c RL l o a d . H ow e v er , t h ei n h e r e n t d y na mi sm i n t h e I M r e s u l t s i n a n i m pr ov edp o we r f a c t o r w i t h P ou t. T h i s i s t h e r e a s o n why t h eS EI G w i t h a n I M l o a d h a s h i g h e r po we r c a p a b i l i t ya n d i mp r ov e d v o l t a g e r e g u l a t i o n t h a n w h i l e l o a de dw i t h a s t a t i c RL l o a d of a p ow er f a c t o r e v e n a sg o o d a s 0 . 8 ; a s sh ow n i n F i g u r e 3 ( d ) . T he v a r i a t i o no f t h e motor s p e e d , n w i t h l o a d i s a l s o s ho wn i nt h e f i g u r e .

I ' A// - 0.6- 0.4- s

~ CWt -0.2.20 ' " lo0 0.1 0.2 0.3 0.4 0.6 OBP (P.U.)Fig 3(b) Variation of Qen er ag Current and Motor Output Power

with Output Power of Generator

VAR and PF (p. u.) c (v, - 1.0

I 2 OIo0 0 2 0.4 0.8 0.8 1 12(P.U.)Fig 3(c) Variation of IM P%r Factor, System var and Capaci tanc e

demand with Power Output

- I -1.2

0.8 PF - LOC * 32.6pF C 32S)LF- 600PF-0.80.8OA t i 3 0 00.2 ' ' l o

0 0.1 02 0.3 0.4 0.6 0.6Po , P.U.)Fig 3(d) Characteristics o SEIG for static and dynamic loads

4.1.2 Motors o f D i f f e r e n t F ra me S i z e sI n o r d e r t o p r o v i d e a g e n e r a l b a s i s o f

i n f o r m a t i o n , f o u r t y p i c a l m o t o r s o f d i f f e r e n tr a t i n g s ( A p p e n d i x - I I ) , a r e c h o s e n f o ri n v e s t i g a t i o n .

F i g . 4 ( a ) sh ow s l o a d c h a r a c t e r i s t i c s of t h eS E I G w i t h m o to r s o f d i f f e r e n t r a t i n g s op e r a t e d fr omn o l o a d to r e s p e c t i v e r a t e d l o a d c o n d i t i o n s . I t i ss e e n t h a t u s i n g a s i n g l e v a l u e d c a p a c i t o r a n dw i t h o u t v i o l a t i n g t h e v o l t a g e a nd c u r r e n t l e v e l s( 1 . 1 0 p . u . a n d 1 . 0 p . u . , r e s p e c t i v e l y ) , t h e SEIG c a ns u p p l y a n I M r a t e d u p t o 5 h p . T h i s m ea ns t h a tu s i n g a s i n g l e v a l u e d c a p a c i t o r b an k t h e SEIG c a ns a f e l y f e e d an I M l o a d o f h a l f i t s r a t i n g .

To i m p ro v e t h e v o l t a g e r e g u l a t i o n o f t h e S EIGv a r i o u s t y p e s o f v o l t a g e r e g u l a t o r s a r e b e i n ge m pl o ye d [ l o - 1 2 1 , w h ic h c o n t r o l t h e v a r s u p p l i e d t ot h e s y s t em w i t h t h e c ha n ge i n l o a d . F i g u r e 4 ( b )s ho ws t h e v a r i a t i o n of c a p a c i t a n c e t o b e e f f e c t e dw i t h t h e l o a d i n o r d e r t o m a i n t a i n t h e t e r m i n a lv o l t a g e a t 1 .0 p . u - f o r f o u r d i f f e r e n t motors .U s i n g s u c h a r e g u l a t o r it i s s e e n t h a t n ow t h e sameSEIG c a n s a f e l y s u p p l y a n I M o f 7 . 5 h p ( 7 5 % r a t i n go f t h e S E IG ) . H ow e ve r, f o r 1 0 h p i n d u c t i o n m o t o rl o a d i t i s s e e n t h a t t h e g e n e r a t o r w in d i ng c u r r e n te x c e e d s i t s r a t e d v a l ue .

vt (P.U.) I (P.U.)1.4 I I S

CurrentOB t

7.6 hp0.2

0 0.1 02 0.3 0.4p0.6 0.8 0.7 0.8 0.0 1 I1M ~ u t (P.u.)Fin 4(a) Characteristic8 of SEI0 for Induction Motor load ofdifferent ratings

00 0.1 0.2 0.3 0.4 0 6 0.8 0.7 0.8 0.0 1 1.1

YAW! (P.U.)Fie.4(b) Capacitance requwement and generator current forInduction Motor load of di fferent ratings

4.1.3 E f f e c t o f P r ime Mover SpeedSo f a r t h e s tu d y i s r e f e r r e d t o a c o n s t a n t

spee d sys tem. SEIGs ar e a l so b e i n g p r o p o se d f o rv a r i a b l e s p e e d W ind E n e rg y C o n v e r s i o n S y s te m(WECS). I t t h e r e f o r e b ec om es r e l e v a n t t o e x a m i n et h e e f f e c t o f v a r y in g p ri m e m ov er sp e e d . F i g . 5 ( a )s ho ws v a r i a t i o n o f V t f o r d i f f e r e n t s p e e d s f o r a 5h p I M l o a d . F i g . 5 ( b ) s ho ws v a r i a t i o n o f t h ec a p a c i t an c e r e q u i r e d t o o b t a i n a n o m i na l v o l t a g e a td i f f e r e n t s p ee d s . A t h i g h e r p r i m e m ov er s p e e d s , al a r g e r v o l t a g e i s g e n e r a t e d a n d po we r c a p a b i l i t y o ft h e S EI G i s e n ha n c e d . F u r t h e r , t h e v o l t a g er e g u l a t o r r e q u i r e d t o m a i n t a in t h e r a t e d t e r m i n a lv o l t a g e w i t h l o a d i n a v a r i a b l e s p e ed s y s t e m s h ou l df o l l o w t h e c h a r a c t e r i s t i c s shown i n F i g u r e S ( b ) .H e n c e , a s u b s t a n t i a l e f f e c t o f s pe e d is n o t i c e d ont h e p e r f o r m a n c e o f t h e SEIG -IM s y s t e m . A g a i n, ac l o s e c o r r e l a t i o n i s s e e n b e t w ee n t h e c o mp u te d a n dt e s t r e s u l t s .


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394

\. l . 0 6 ]0.8 -1.y t 0.860.8I0.40 0.2 0.4 0.0 0.8 1 1.2 1.4 1.8

kcul (P.U)Fig 5(a) Effect of Prime Mover S b e d on Terminal Voltage

c ()v)vt - 1.0 p.u. y 1.06TO

-$- 0.96

40

90IIIIIIIIIIIIII0 0.1 02 0.9 0.4 O b 0.0 0.7 0.8 0.Q 1 1.1 12%,,ut (P.U.)Fig 5(b) Effect Prime Mover Speed on Capacitance requirement

4. 2 Starting of an Induction Motor on an SEIGHaving studied th e steady state operation ofthe SEIG-IM system, it becomes desirable to lookinto sta rting of an IM on an SEIG.It is found that to start a 5 hp motor on a7.5 KW SEIG, a much larger capacitance (107 P F ) isrequired as compared to the capacitance (50 P F )r e q u i r e d f o r t h e s t e a d y - s t a t e op e r a t i on . . T h i svalue of capacitance ca n be obtained by using th ea l r e a d y p r o p o s e d a l g o r i t h m w i t h a s l i g h tmodification. Here, the equivalent circuit of themotor i n Figure l(c), will now correspond to s = 1(i.e. block rotor condition). Thus, this blockrotor equivalent circuit of motor can be convertedinto an equivalent RL load. Now for this load, them i n i m u m c a p a c i t a n c e r e q u i r e d f o r e n s u r i n g s e l fexcitati on can be calculated ( 5 1 .It is also noticed that for very sma ll motors(112 hp and 1 hp), the capacitance required for thesteady state operation is also sufficient for thestarting.T o t e s t e f f e c t i v e n e s s o f t h e a l g o r i t h m i nchoosing the valu e of capacitance to satisfactorilystart the induction motor on the SEIG, variousswitching operatio ns were performed. Measurem entswere tak en of the termina l voltage, th e generators t a t o r c u r r e n t a n d t h e l o ad c u r r e nt . A n X- Yrecorder interfaced to a CR O was used to reproducethe switching transients, which are shown inF i g u r e 6. T h e s e f i g u r e s c o r r e s po n d t o t h efollowing sequence of operation.i

ii

Self Excitation: The SEIG was driven at thes y n c h r o n o u s s p e e d a n d a d e l t a c o n n e c t e dcapacitor bank of 50 pF/phase was switched onto the ter minals of th e machine. 5 0 pF/phasec a p a c i t a n c e c o r r e s p o n d s t o t h e s t e a d y - s t a t erequiremen ts of the 5 hp IM.Motor Starting: Once the machine reached thesteady-state self-excited condition, the 5 hpIM along with a delta connected capacitor bank(57 )cF/phase) was switched on to the terminalsof the machine.As the induction motor picked up speed and thes y s t e m a s s u m e d i t s s t e a d y - s t a t e , t h e 5 7kF/phase capacitor bank was taken off.

iii

iv

Switching-in of Additional Motor: As the SEIG-IM system got stabilized, an additional 1 hpmotor was switched on to the system. This wasdone to simulate a multi-motor system.Load Rejection: A s the SEIG-IMs system settledto the new steady state condition, both motorswere simultaneously taken off leaving the SEIGoperating with only 50 pllphase capacitor bankconnected across its terminals.S i n c e a 2 - c h a n n e l C R O w a s u s e d , i t w a s

possible to record only two signals at a time.Hence, every switching action was performed twice,due to which the switching instants in Figure 6 (c)are not properly synchronized with those of Figures6(a ) and 6(b).It is observed that during various switchingoperations, the SEIG assumes the new steady stateo p e r a t i n g c o n d i t i o n w i t h o u t l o o s i n g s e l f -excitation. Further, the current and the voltageovershoot s are found to be within th e tolerablelimits. These observations thus demonstrate theeffectiveness of the algorithm in calculating thevalue of starting capacitor and also the ability ofthe SEIG to sustain IM switchings.It may be noted that the prediction of th evalue of starting capacitor is based on the steady- state analysis. Fo r a detailed study of theswitching operation, transient analysis should bedone, whic h is beyond the scope of the presentp a p e r . T h e v a r i o u s s w i t c h i n g r e s u l t s s h o w n a r emainly aimed at assessing suitabil ity of theSEIG-IM system in lower ratings, where direct online (DOL) switching is used. In higher ratingswhere soft switching of motors is desired, thestarting capacitor may not be required.The authors have been engaged to develop anSEIG-IM system for low power agri cultural pumpingapplicati on using micro-hydel and wind energy inlower ratings (up to 50 kW). The proposed analysist h u s s u g g e s t s f e a s i b i l i t y o f a n S EI G - I M s y s t e mh a v i n g t w o s e t s o f c a p a c i t o r b a n ks . O n e i scontinuously rated for the running operation, whilethe other is short time rated for starting of t heIM. The latter is to be removed once the IM picksup speed. The values of these capacitors can beobtained from the proposed analysis as discussedbefore. The steady state analysis gives the valueof the starting capacitor that can satisfactorilys t a r t t h e m o t o r . I n a p p l i c a t i o n s w h e r e t h einductio n motor rating is much lower than that ofthe generator, the system can do away with ther e q u i r e m e n t o f s t a r t i n g c a p a c i t o r . A l t h o u g h ,transien t analy sis is not carried out in the paper,t h e e x p e r i m e n t e d r e s u l t s d e m o n s t r a t e t h ef e a s i b i l i t y o f t h e s y s t e m t o wi t h s t a nd t h eswitching transients as severe as that due t o thestarting of induction motors.

5 . CONCLUSIONDetailed analysis of the SEIG feeding power toa dynamic load (induction motor) is presented.

An algorithm is proposed for the prediction ofsteady sta te performance of the SEIG-IM system.Theoretic al resu lts are presented for a variety ofoperating conditions along with the experimentalo n e s ; a n d a c l o s e a g r e e m e n t h a s b e e n o b s e r v e dbetween the two. Salient observations with regardto the IM load have been extensively discussed.The steady state analysis is extended t o determinethe value of capacitor required for the starting ofan induction motor. Various experimental resultsa r e p r e s e n t e d f o r a s e q u e n c e o f s w i t c h i n goperations. Based on the analysis, the suitabilityof the SEIG for dynamic loads has been illustrated.Design of an SEIG-IM system for low power pumpings y s t e m h a s b e e n p r o p o se d . E f f e c t o f s p e e d


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I

t l . O 1 ii i i iFig. 6 Switching transients of SEIG-IM system

variation on th e performance of the SEIG-IM systemhas been briefly discussed.to cover a range of standardseem to confirm t he generalF o l l o w i n g s a r e t h e m a i ninvestigation.

The study is extendedmotors and the resultstrend presented here.o b s e r v a t i o n s o f t h e

1.

2.

3.4.

5.

Using a sing le valued capacitor bank (i.e.without a voltage regulator), an SEIG can safelysupply an Induct ion motor rated upto 50% of itsown rating.Using a voltage regulator that maintains therated termi nal voltage, an SEIG can safely feedan induction motor rated upto 75% of its rating.The SEIG can sustain the starting transients ofth e IM without losing self excitation.The proposed algori thm is effective not only inpredicting the performance of an SEIG-IM systembut also in calculati ng the value of capacitancerequired for the starting of the motor.It is possible t o design an SEIG-IM system usingtwo sets of capacitor banks (for starting andrunning), for low power agricul tural pumpingSystem, with ratings of the SEIG and the IMbeing in a ratio of 2:l.

[41

[51

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N. H. Malik and S. E. Haque, "steady Stateanalysis and performa nce of an +,solateds e l f e x c i t e d i n d u c t i o n g e n e r a t o r , IEEETrans. on Ener gy Conversio n, vol. EC-1,no.3, pp.133-139, Septemb er 1986;N. H. Mal ik and A.A. Mazi, Capaci tancer e q u i r e m e n t s f o r i s o l a t ed s e l f e x c i t e dgen er ato rs ", ibid, vol. EC-2, no. 1, pp. 62-69March 1987.Y. Uct ug and M D e m i r e l k e r , " M o ~ e l l i n g ,analysis and control of wind turbine , Proc.C. G r a n t h a m , D . S u t a n t o a n d B. M i s m a i l ,"St ea dy st at e and Transien:, Ana lys is of Sel fExcited Induction Generato r ,ibid. pt B, vol.S. P. Sing h, Bhim Sinq h and M. P. Jain," P e r f o r m a n c e c h a r a c t e r i s t i c s a n d o p t i m u mutilization of a cage machine as capacitorexcited induction ge nerator", paper no. 9 0SM 284-0 EC, pr esen ted at th e IEEE/PES 1990Summer Meeting, Minnesota,l990.r e q u i r e m e n t f o r I s o l a t e d S e l f E x c i t e dInduction Generator" Proc. IEE, pt B, vol.137, pp. 155-160, 199bD. U. Nov otn y, D. J. Gritt er and G. H.S t u d s , "Se f ex t at ion in invert erdri ve n ind uct ion machin e", IEEE Trans. onPo we r Appara tus and System s, vol. PAS-96,J. Arrillaga and D. B. Watson, "Sta tic powe rc o n v e r s i o n f r o m s e l f ex c i t e d i n d u c t i o n

IEE, pt C, vol. 223, pp. 268- 275, July 1988.

136, pp 61-68.

A1 Jabri A. K. and Alol ah A.I., "Cap acit ance

ge ner at ors " Proc. IEE, vol. 125, no. 8,6. REFERENCES pp. 743- 746, August, 1978.no. 4, pp. 1117-1125, July/August 1977D Bes set t and F. M. Pot ter , "Ca pac it ive Elder, J.T. Boys, J. L. Woodward,Eici;ation for in duc ti on gene rato r", AIEE excited induction machine as low costgenerator", ibid, v o l . 131, pt. C, no. 2, PP.rans., pp. 540-5,45, May 1935.[21 B. C. DOX ey, Th eo ry and ap pl ic at io n o f 33-40, March 1984.capacitorexcited inducti on generator*, The [13] :.S. Murthy, C.S. Jha and P. S. Nagendra Rae,A n a l y s i s o f g r i d c o n n e c t e d i n d u c t i o nngineer, no. 29, pp. 893-897, Novem ber i963.[31 S. S. Mu th y, 0.P.Malik. and A . X. Tandon gene rato rs driven by hydrolwind turbines under"A na ly si s of self- excite d ind uct ion realistic system constraints", IEEE Trans. onEnergy Conversion , vol. 5, no.1, PP. 1-7,en er at or s" Proc.IEE, vo1.129, pt. C. no. 6,pp. 260-265,' 1982. Marc h 1990


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APPENDIX - IAlgorithm for obtaining operating XMm and s

1. Read motor parameters, magnetizationcharacteristic (variation of XMm with V IF andg2.3.4.5.6.

XMmo (no load value).Mout 'Set XMm =Calculate s for the given PMout.[131For this s,Obtain Xm corresponding to VMUpdate Xm and repeat from jtep 3unless difference in Xu, between two

find VMg = Vt - Is 54sto Step 5successiveiteration is less tha;;" a small quantity (say1.OE-03) .

APPENDIX -11Details of Induction Motors at 50 Hz

IEC Power volt Current stator r/minFrame hP1kW V A Winding80 110.75 415 1.7 Star 2800l0OL 312.2 415 4.9 Delta 1410ll2M 5j3.7 415 7.6 Delta 1430132s 7.515.5 415 11 Delta 1450132M 1017.5 415 14 Delta 1450

BIOQRAPHY-. S h r i d h a r ( S t u d e n t M e m b e r ) w a s bo r n i nBhilainagar, MP (India) in 1966. He received hisB.E. degre e from Maulana Azad College ofTec hno logy Bhopal, and the M.Tech degree fromInstitute bf Technology -8anaras Hindu University,Varanasi.H e j o i n e d t h e d e p a r t m e n t o f e l e c t r i c a lenginee rin Indian Institute of Technology, Delhiin July 1986 and is presently, a full time researchscholar with the department working, towards hi sPh.D. degree. Hi s are as of interest are computerbased analysis and design of electrical machinesand their efficient energ y conversion andapplica tion in non-conventional power plants.

--r. Bhim Sinah, wa s born at Rahamapur in U.P. in1956. He receive d his B.E. degree from RoorkeeUniver sity, and M.Tech and Ph.D. degre e from IIT-Del hi in 1977, 1979 and 1983 respectively.From 1983 to 1990 he was with the department ofelectr ical engineering, University of Roorkee. Atpresent he is Assistant Professor at IIT Delhi.He has over 80 papers to his credits in the fieldof CAD, Power Electronics and Analysis and Controlof Electrical Machines.Prof. C. S Jha, was born at Vijainagar in Bihar(India) in 1934 and educated at Patna University,IISc, Bangalore, Heriot Watt College, Edinberg(U.K.), and Bristol University ( U . K . ) . Has been aProfessor of Electrical Engineering at IIT Delhisince 1964.He has made significant contributions in electricalmachi ne theory and application and published alarge number of papers. He has been involved in th eplanning and administration of technical educationin India sin ce the early 1970s. He was Director ofthe prestigious IIT at Kharagpur (1974-78), wasEducational Advisor t o the Government of India ontechni cal education planning and has been active incurriculum planning and development of engineeringeducati on in India. He has been Visiting Professorat many universities in the West, a member of th eboard of Trustees of Asia Institute of Technology,B a n g k o k ( 1 9 7 4 - 8 6 ) a n d i s a m e m b e r o f U N E S C Ointernational meeting group on continuing educationof engineers since 1975.At present, he is the Vice Chancellor of theBanaras Hindu University at Varanasi.--rof. B.P. Si nah was bor n in Singhiy a, in 1940. Hereceiv ed his B.Sc. (Engg. ) degree in 1963 fromBITS, Sindri , ME in Electri cal Engg. in 1966 fromCalcut ta Univers ity and PhD in 1974 from IIT Delhi.He was a Senior Fellow at BE College, Howrah (1963-1966) and after serving MIT Muzaffarpur as afaculty member for over a decade (1966-78), hejoined IIT Delhi in 1978, where he is a Professorwith th e Dept. of Electrical Engg. He was avisiting Professor at California State University,Long Beach during 1988 to 1990.His research interests are in design, analysis andcontrol of electrical machines.

analysis of self excited induction generator

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